1. Field of the Invention
The present invention is directed toward an electric heating apparatus and, more particularly, to an apparatus having a resistance wire with an in-line thermostatic electric current control element.
2. Related Art
Electric heater assemblies having a resistance wire with in-line thermostats are known in the art. A widely used example of such heater assemblies employs a thermostat with a pair of terminals, each having a right-angled bend, with the right-angled portion of each being secured by a pair of threaded nuts to the threaded distal end of a mounting screw. Typically, there is a lock washer on all contacting faces of the threaded nuts.
One example of this prior art arrangement is disclosed in U.S. Pat. No. 3,770,939 (the ""939 patentxe2x80x9d), and is shown in prior art FIGS. 1A, 1B and 1C of this disclosure. Referring to the prior art FIG. 1A, and the enlargement of its region 1B shown by FIG. 1B, the prior art thermostat 10 has terminal flanges 14 and 16 extending therefrom, each having proximal and distal portions, labeled as 14A and 14B, and 16A and 16B, respectively. Distal portions 14B and 16B extend at right angles from their respective proximal portions 14A and 16A. Viewed from the FIG. 1B side projection AA, which is shown in FIG. 1C, the distal portion 16B has a U-shaped cut-out portion 16U, as does 14B (not shown).
As shown in prior art FIG. 1A, a ladder frame 17 supports a resistive wire heating element 18 using a plurality of first tubular insulating bushings 20. The bushings 20 are typically formed of ceramic. The frame 17 also supports a pair of second tubular insulating bushings 22 and 24.
Referring to prior art FIG. 1B, a first thermostat wire connection screw 26, having a head 26A and a threaded distal end 26B, extends through the first ceramic thermostat support bushing 22. Likewise, a second thermostat wire connection screw 28 extends through the second ceramic thermostat support bushing 24. A heater resistance wire end portion 30 is welded to the head 26A of the first screw 26. A first threaded nut 32, with an associated lock washer 34 secures the first screw 26 to its ceramic bushing 22. The second thermostat mounting screw 28 is secured to its corresponding bushing 24 by a second threaded nut 36 and associated lock washer 38.
As shown in the prior art FIG. 1B, a fuse element 40 connects to the head 28A of the second thermostat mounting screw by welding or by wrapping the connecting end 40A of the fuse under the screw head 28A, before tightening the second threaded nut 36. If the connecting end is wrapped under the screw head, as in FIG. 1B, a flat washer 41 is preferable.
The thermostat 10 within prior art FIGS. 1A-1B is mounted as follows:
The first and second thermostat mounting screws 26 and 28 are secured to their respective bushings 22 and 24 by tightening the first and second threaded nuts 32 and 36. After this assembly, a spacing A is between the inner faces of the first and second threaded nuts. Referring to FIG. 1B, the distance labeled Axe2x80x2 is from the distal portion 14B of the first flange 14 of the thermostat 10 to the distal portion 16B of the second flange 16. The dimension Axe2x80x2 is slightly less than A. Referring to FIG. 1C, which depicts the U-shaped cutout 16U of the second flange 16, the cut-out is shaped and dimensioned to accommodate the threaded portion 28B of the second screw 28. Likewise, the cut-out (not shown) in the first flange 14 accommodates the threaded portion 26B of the first screw 26. Because of the dimensions A and Axe2x80x2, and the U-shaped cutouts in the thermostat flange distal portions 14B and 16B, the thermostat 10 can be placed into the position shown in FIGS. 1A and 1B. After such positioning the distal portion 14B of the first flange 14 of thermostat 10 is secured by a third nut 42, typically with a pair of lock washers (not shown), one on each side of the distal portion 14B flange. In a mirror arrangement, the distal portion 16B of the second flange 16 is secured by a fourth nut 44, also typically with a pair of lock washers (not shown).
Although the above-described prior art structure mounts the thermostat 10 to the frame 17 in line with the heating element, there are shortcomings. One is the number of parts, namely six lock washers, one flat washer, four threaded nuts, and two screws. This quantity of parts creates and carries numerous costs, including vendor selection and monitoring costs, inventory costs, and quality control costs.
Another shortcoming is that the manual labor required to assemble its plurality of parts is time intensive. More specifically, the nuts 32, 36, 42 and 44 must be hand tightened by applying repeated short swing rotations with a small open-ended wrench.
Another shortcoming is that the heater resistance wire end portion 30 is welded to the head 26A of the first screw 26, and typically the welding is performed before the thermostat 10 is installed. Still further, the end of the fuse element 40 must be bent in two in two planes using an off-line subassembly operation such as, for example, hand-bending with a pair of needle-nose pliers, to properly wrap the end around the screw head 28A. This bending operation adds manufacturing cost.
Referring to prior art FIGS. 1A-1B, still another shortcoming with such structure is that external connection terminals 46 are typically supported by third bushings 48. The third bushings 48 are different from the second bushings 22 and 24 which support the first and second thermostat screws 26 and 28. The result is a further increase in the parts count.
An object of the present invention is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat having a reduced parts count as compared to the prior art.
Another object is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat that is easier and quicker to assemble than the thermostat mounting apparatus of the prior art.
Still another object is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat and an in-line fuse, with a mounting structure for the fuse having a reduced part count as compared to the prior art.
Another object is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat and with external connection tabs mounted to the frame, where the thermostat and connection tab mounts employ identical components.
Yet another object of the present invention is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat, employing a standard thermostat with flat terminals which have a threaded hole added for accepting a screw.
Still another object of the present invention is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat, with a thermostat mounting structure that does not require welding attachments to the thermostat terminals.
A further objective of the present invention is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat, employing uniform flat profile terminals for crimping to resistance wire ends and fuse wire ends, and for functioning as external electrical connection tabs and for single-screw attachment to the thermostat terminals.
Related to the above-identified objective, a still further objective is a structure for accommodating and mounting an in-line thermostat in a selectable rotational orientation. The selectable orientation provides improved access for servicing and replacing the thermostat in an installed heater assembly.
An example embodiment of the invention includes a metal frame supporting a plurality of first insulators supporting a heater element resistance wire. The frame further supports a pair of thermostat support insulators, or bushings which, in turn, support a pair of thermostat mounting blades. A thermostat having two extended terminals is secured to the pair of thermostat mounting blades, by one threaded screw attaching one thermostat terminal to a first of the thermostat mounting blades and by one threaded screw attaching the other thermostat terminal to the other thermostat mounting blade. Each of the thermostat mounting blades has a longitudinal axis, with an outer crimping portion at one end and a screw tab at the other. The screw tab includes a through hole for engaging or accommodating the threaded screw attaching the thermostat mounting blade to the thermostat terminal. Each of the thermostat mounting blades further includes an axial abutment to limit insertion into the thermostat mounting insulator.
The first thermostat mounting blade is crimped onto an end of the resistive wire and inserted into the first bushing until the axial abutment is against the outer face of the bushing and the screw tab, with its through hole, protrudes from the inner face of the bushing. Likewise the second thermostat mounting blade is crimped onto an end of a fuse or other conductive element and inserted into the second bushing until the axial abutment is against the outer face and the screw tab protrudes from the inner face. The thermostat is then connected, using one screw for each terminal flange, to the protruding screw tabs of the terminal mounting blades. The assembly of the thermostat and the pair of terminal mounting blades is thus secured, in an axial direction, within the pair of bushings by the axial abutment of the first terminal mounting blade being against the outer face of the first bushing and the axial abutment of the second terminal mounting blade being against the outer face of the second bushing.
A further embodiment of the invention includes a bendable securing abutment disposed on the tab portion of the thermostat mounting blades. The bendable securing abutment is disposed to be exposed past the inner face of the bushing after the thermostat mounting blades is inserted through the center hole such that the axial abutment is against the outer face of the bushing. The bendable securing abutment is then bent or otherwise deformed to have a height greater than the height of the through hole of the bushing. Each thermostat mounting blade is thus secured against axial movement by the contact of its axial abutment against the outer face of the bushing it is inserted through, and by the bendable securing abutment being against the inner face of that bushing.
A still further embodiment includes a thermostat mounting bushing having a through hole that accommodates the thermostat mounting blade in more than one rotational orientation about the blade""s longitudinal axis. This provides for mounting the in-line thermostat in a selectable rotational orientation. The selectable orientation provides improved access for servicing and replacing the thermostat in an installed heater assembly. An example of this embodiment is a thermostat mounting bushing having a first and a second through hole. The first through hole accommodates the thermostat mounting blade, or other hardware, in a first or second orientation, the second being 180 degrees relative to the first. The second through hole has a cross-sectional profile the same as the first, and has the same longitudinal axis as the first but is rotated by, for example 90 degrees. The second through hole accommodates the thermostat mounting blade in a third and fourth orientation, the fourth being 180 degrees relative to the third. The first and second through holes thereby permit four orientations of the thermostat mounting blades and, thus, four rotational orientations for mounting the thermostat or other hardware.
The apparatus of this invention provides significant reduction in the number of parts required to connect the thermostat to the electric heater assembly.
The invention also, by using simple crimping of the thermostat mounting blades onto the resistive wire or other elements, and then insertion into their support bushings followed by single-screw attachment to the thermostat terminals, reduces the amount of time and difficulty associated with manual assembly of the in-line thermostat to the electric heater assembly.